Fukushima Watch: What’s Different About the Latest Radioactive Leak Into the Sea

By Moeko Fujii and Phred Dvorak

Fukushima watchers may be forgiven for feeling a sense of déjà vu, after the operator of the damaged Fukushima Daiichi nuclear power plant said that radioactive water could be leaking into the ocean. After all, anyone who’s been following the state of the plant since the terrible nuclear accident in March 2011 knows Tokyo Electric Power Co. has said many times before that leaks from buildings or trenches may have spilled contaminated water into the sea.

European Pressphoto Agency

The contaminated water being extracted from a manhole at the crippled Fukushima Daiichi nuclear power plant on July 17.

So what’s the difference between what Tepco is reporting now, and all those other leaks and spills readers may remember from the past? This time, for the first time, the company doesn’t yet know where the water is coming from.

That lack of a precise source of contamination, plus data showing a probable connection between groundwater and seawater in that area, is prompting Tepco to say for the first time that the radioactive water may be seeping directly out of the ground near the ocean.

First a bit of background to put the problems in perspective:

The current investigations started in May, when Tepco found that levels of the radioactive element tritium in test wells near the ocean had climbed 17 times higher than they were in December. That prompted the drilling of more wells and more tests. By early July, Tepco’s surveyers were finding levels of tritium as well as radioactive cesium rising at a very fast clip.

The findings led Japan’s Nuclear Regulation Authority to raise concerns on July 10 that the radioactive water could be flowing into the Pacific, although at the time Tepco said there was no evidence of that.

But on Monday, Tepco said that data it collected showed the levels of the water in its test wells was rising and falling along with sea-water levels, according to the tides. That led the company to conclude that there could indeed be a link between the groundwater at the coastal side of the plant where the wells are, and sea water.

Tepco said it is still unclear whether the contamination is from the radioactive fallout in the immediate aftermath of the disaster, or more recent leaks from other sources. The level of radiation in the sea water near the mouth of the harbor is very low, and thus contamination is currently limited to the water near the plant, Tepco officials said.

“We have been working on containment to prevent water from spreading outside the site. We can only say we are very sorry,” a Tepco spokesman said at a Monday press conference.

This is quite different from previous episodes of contamination. Before the current findings, Tepco has had four major episodes of radioactively contaminated water leaking into the sea (as well as a couple of times when the utility–pressed for storage space–just dumped it).

In all four of those cases, however, the company was able to pinpoint the likely source of the problem, and plug it up. Here’s JRT’s recap:

March/April 2011: The month after the accident, when three of Fukushima Daiichi’s reactors melted down, was likely the worst in terms of oceanic contamination. Tepco officials said hundreds of tons of highly contaminated water–probably used to cool the overheating reactor core of Unit No. 2–flooded a nearby turbine building and flowed into the ocean through a utility trench. The company estimated some 500 tons of contaminated water may have gone into the sea over the course of five days, until a crack in a containment pit by the shoreline was plugged with a gel-like sodium silicate. The water had an iodine-131 concentration of 5.4 million becquerels per cubic centimeter, about 100 million times the legal limit, according to Tepco.

May 2011: Tepco said an additional 250 tons of water may have leaked into the ocean from Unit No. 3. Within seven hours of finding the water source in a pit near the water intake canal, they were able to stop the outflow by filling it with concrete.

December 2011: A pool of about 45 tons of contaminated water was found around a condensation unit used by a water-purification system, leaking about 150 liters of processed water into the sea through a ditch connected with the beach. This water was contaminated with high levels of strontium.

April 2012: A leak from a pipeline that carried concentrated radioactive water from a desalination device to a storage tank may have dumped an estimated 12 tons of contaminated water into the ocean, until it was stopped 30 minutes later by closing some valves. High levels of cesium 134 and 137 were confirmed at the point of the leak, roughly 300 yards from the ocean, but no detectable amounts of radioactive contamination were found in the sea water.

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